Question

Thanks for taking the time to read this. I am a registrar from South Africa with an interesting young patient in whom your opinion would be greatly Appreciated. This young male first presented as a neonate with congenital hypothyroidism. At that time a thyroid uptake scan showed no thyroid tissue anywhere and a diagnosis of congenital thyroid agenesis was made. He was started on thyroxin, followed up for a while, and then was lost to follow up.

A few years later he returned to the clinic with a mass in the neck which clinically appeared to be a thyroid mass! Reviewing his initially uptake scans showed no uptake, and a repeat isotope scan again showed no uptake, however an ultrasound of his neck showed a multinodular thyroid gland. Too cut a long story short, he was found to have follicular Ca ofthe thyroid (most likely due to unsuppressed TSH) and a total thyroidectomy was performed. The diagnosis was then altered from thyroid agenesis, to an Iodine trapping defect or some form of dyshormonogenisis as uptake scan remained completely negative. He was treated with thyroxine post operatively and again absconded from follow up.

He is now 15yrs old. Of normal height and weight for his age, and has returned to our services with a lump in his neck. He is otherwise asymptomatic. A Fine needle aspiration of the lump (which is a lymph node in the cervical chain) shows follicular cells and the presumption is that the follicular Ca ( which on initial removal had extended through the thyroid capsule and invaded the vessels) has disseminated. A SPECT scan has shown uptake in a chain of lymph nodes in the neck extending into the thorax.

My question is: In lieu of his iodine trapping defect it will not be possible to treat this with Radio-active iodine, do you have any suggestions in management of this young man.

Kind regards,

Jonathan Mervis (Paediatric Registrar)

Response

This is a very interesting and intriguing case. I can try some comments.

Iodine trapping defect can cause hypothyroidism but is always associated with goiter. Thus this cannot be the cause of the patient's congenital hypothyroidism, unless in addition the patient had also an other genetic defect responsible for thyroid agenesis (such as absence of thyroid specific transcription factor TTF1,2 or others).

Whatever the reason for his thyroid agenesis, I guess that it was not a complete agenesis, but rather the patient might have some small thyroid tissue not visible in the scan. The follicular tumor may have developed from this remnant.

Another possibility to explain the lack of uptake (is this true also in the metastatic tissue? this is not clearly stated in your report) may be a defective TSH or a TSH-receptor. Measurement of serum Tg (and Tg immuno-staining in the tumor tissue) would also be interesting to know.

Regarding treatment, I think that I would try stimulation with recombinant human TSH (Thyrogen) to see whether it is possible to elicit iodine uptake and Tg production. A part from that I think that surgery is the only other option.